Drawing Out the Facts

The STEM Chicksmas Day Ten: Graphene

For the 12 Days of “The STEM Chicksmas” we’re highlighting 12 scientists who have contributed something innovative and exciting to their field. It is the season of giving, and these brilliant minds have given incredible gifts to the scientific community! This year we’re looking at 12 Nobel Prize winners from the past 15 years in the fields of Physics, Chemistry, and Physiology or Medicine.

What if you could win a Nobel Prize with a pencil and some tape? The winners of the 2010 Nobel Prize Andre Geim and Konstantin Novoselov did just that. They isolated and characterized a structure called graphene from graphite, the stuff pencils are made from, discovering a new class of stable “two dimensional” materials.

Graphite is a layered material, unlike other crystal lattices which are made of unit cells that extend in three dimensions. Each layer of graphite is made up of carbons arranged in repeating hexagons, like a honeycomb. The layers are held together by van der Waals forces, which are relatively weak interatomic interactions. Scientists have been trying for decades to isolate a single layer of graphite, called graphene, without success. Geim and Novoselov succeeded through a simple method called “exfoliation.” You lay a piece of scotch tape down on a piece of graphite. You then stick and unstick the scotch tape with a second piece of scotch tape over and over, each time yielding fewer layers of carbon, until you have a single layer. The mechanical strength of sticking and unsticking the tape is enough to overcome the van der Waals interactions without disrupting the stronger covalent bonds within the layer. This layer is “two dimensional”—it has macroscopic width and length, but it is only one atom thick. Consequently, its properties only extend in two dimensions, making it for all intents and purposes two dimensional.

Geim and Novoselov’s method was also remarkable because of the surface area it was able to produce. They were able to produce reliably large areas of intact graphene with few or no defects. Because of this feat, they were able to characterize their material and perform various tests on it. They discovered that graphene is conductive (read more about conductivity in our post on conductive polymers). Graphene is also very mechanically strong. A common example people use is that a single sheet of graphene is strong enough to hold up a cat! At least, according to calculations, because we’ve never produced a sheet large enough to try. It is very flexible, partially because the intralayer bonding is so strong. Graphene is also almost transparent.

Graphene’s unique properties make it the source of a lot of research into future applications. One example is organic solar cells. Graphene is basically transparent, so it could be coated onto more conventional solar panels without preventing light from going through, and contribute its conductive properties to enhances the solar cell’s energy conversion efficiency. Another potential application is in electronics—we could use graphene to make flexible conductors. The future of graphene is very exciting and a common subject of research in materials and condensed matter physics. However, because it is currently impossible to produce industrial sized layers of graphene (the “large” layers mentioned earlier are a few microns wide), many of these applications remain theoretical. The discovery of graphene also showed that it is possible to make stable two dimensional materials, which was previously thought of as impossible. Two dimensional materials is a rising field that many scientists are studying intently (including this author’s former research group!).

The discovery of graphene has opened up exciting new research and pioneered new paths. However, best of all, it shows that science doesn’t always need fancy and expensive equipment—sometimes all you need is some household objects and ingenuity.

Read more at the Nobel Prize website or read the award winning work here.